A measuring apparatus is calibrated before measurement in order to accurately measure the properties of a device under test. The calibration of an apparatus for measuring the output signals of a device under test involves applying reference signals to a defining plane and monitoring these reference signals on the side of the measuring apparatus. A variety of signal sources can be used for the reference signal source, depending on the subject of the calibration. For instance, a high-precision, direct-current source is used to calibration direct-current accuracy. Moreover, a high-precision, sine-wave signal source is used to calibrate frequency properties. A high-precision pulse source is used to calibrate timing. A high-precision pulse source is also used to calibrate frequency properties (Kiyo Hiwada and Toshio Tamamura, “Dynamic Test System for High Speed Mixed Signal Devices,” Transactions of International Test Conference, 1987, pp. 370-375.).
However, the terminals of the device under test are of various shapes and dispositions and there are therefore cases in which the measuring apparatus and the device under test are connected by a tool or interface, and the like. For instance, a semiconductor tester is used for a variety of devices under test; in such cases, it comprises a board that serves as an interface with the device under test and the main part of the measuring apparatus. The board can be a DUT board (device under test board) or a load board. Reference signals must be applied to the terminal of the device under test or close to this terminal in order to eliminate the measurement error attributed to the signal path between the device under test and the measuring apparatus. However, this is technologically difficult. For instance, a switch must be placed between the device under test and the measuring apparatus in order to apply reference signals close to the terminal of the device under test. In this case, the switch becomes a cause of measurement errors and these measurement errors cannot be eliminated by calibration. When reference signals are applied close to the terminal of a device under test of a semiconductor tester, the reference signals pass through the board. However, the board is the region that is free for the user and cannot be used by a system manufacturer; therefore, application of reference signals close to the terminal of a device under test is essentially impossible.
It should be noted that timing errors attributed to the signal path from the device under test to the measuring apparatus can be eliminated by TDR without applying signals near the terminal of the device under test (for instance, refer to JP Unexamined Patent Application (Kokai) 11[1999]-190,760 (page 2, FIG. 3)). This TDR method can only be used for the timing calibration of digital signal systems and cannot be used to calibrate other parameters, including analog system timing.